compat: work around the lack of configoverride in mercurial 4.0 The phase preservation will stay broken on 4.0 and below

compat: add an abstraction for 'scmutil.cleanupnodes' The usage of the function was added in 103244e34a9c but is not compatible with Mercurial <= 4.2.

compat: conditionally access config item Version 4.2 and below do not have config items support. So the extensions helper do not register anything.

compat: handle version where obsutil is not available Version older than 4.3 is do not have the obsutil option. We need to handle that.

test: use node instead of rev in topic push tests This makes the test more stable when revision number changes.

test: use node instead of rev in uncommit -i test This makes the test more stable when revision number changes.

branching: create the mercurial-4.3 test compatibility branch This branch will contains the expected test output with 4.3.

branch: merge with stable to prepare 6.7 release In addition, Mercurial 4.4-rc is out, so we need to update the expected output.

changeloge: add details about topic-mode

effect-flag: remove wrapping of createmarkers for Mercurial 4.4 Now that effect-flag has landed in Mercurial 4.4, we don't need to wrap createmarkers for this version anymore.